Transmission pump drive

ABSTRACT

A pump drive for a vehicle transmission pump. A transmission input torque member is operable to carry prime mover torque. A source of pump torque includes a pump input torque member circumscribing the transmission input torque member to apply torque to the transmission pump. An overrunning clutch is interposed between the pump input torque member and the transmission input torque member to carry the prime mover torque from the transmission input torque member to the pump torque output member.

FIELD OF THE INVENTION

The present invention relates generally to vehicle powertrains, and moreparticularly to a vehicle transmission including a pump.

BACKGROUND OF THE INVENTION

Vehicle transmissions typically include one or more pumps to deliverpressurized hydraulic fluid for lubrication and actuation oftransmission shift elements. These transmission pumps are typicallydriven by torque from an engine coupled to the transmission. In some ofthese transmissions, the pumps are operable to maintain oil pressure inthe transmission even when the engine is idled or stopped. One suchtransmission may include a main pump and an auxiliary pump, which addsweight, cost, and complexity. Another such transmission may include twoor more overrunning clutches to carry torque from the engine and anauxiliary electric motor to a single transmission pump. The lattertransmission uses multiple overrunning clutches, undesirable low voltagecontrol connections to the electric motor, expensive speed and positionsensors, and/or complex motor position sensing techniques.

SUMMARY OF THE INVENTION

In one implementation of a presently preferred pump drive for a vehicletransmission pump, a transmission input torque member is operable tocarry prime mover torque. Also, a source of pump torque includes a pumpinput torque member circumscribing the transmission input torque memberto apply torque to the transmission pump. Further, an overrunning clutchis interposed between the pump input torque member and the transmissioninput torque member to carry the prime mover torque from thetransmission input torque member to the pump torque output member.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of preferred embodiments and bestmode will be set forth with reference to the accompanying drawings, inwhich:

FIG. 1 is a block diagram of an embodiment of a vehicle powertrain;

FIG. 2 is a cross-sectional view of an embodiment of a transmission pumpdrive of the vehicle powertrain of FIG. 1; and

FIG. 3 is a schematic diagram of an embodiment of a brushless directcurrent motor arrangement for use with the transmission pump of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring in more detail to the drawings, FIG. 1 illustrates anexemplary vehicle drivetrain 10 that delivers torque to vehicle wheels12 for driving a vehicle. The drivetrain 10 includes an exemplary primemover 14 to provide prime mover torque for the drivetrain, and anexemplary transmission 16 to receive the prime mover torque and convertit to, and transmit it as, transmission output torque. The drivetrain 10can also include an exemplary differential 18 to receive thetransmission output torque, and convert it and redirect it to the wheels12. The prime mover 14 can be an internal combustion engine, electricmotor, or any other suitable device to generate torque. The prime mover14 includes an output shaft 20 such as a crankshaft, rotor shaft, or thelike. Similarly, the differential 18 can include output shafts 22 andcan be a rear-wheel-drive rear axle, a front-wheel-drive final driveunit, or any other suitable device to convert, transmit, redirect, orotherwise carry torque. Those skilled in the art will recognize that anyother suitable drivetrain configuration can also or instead be used withthe novel aspects of the transmission structure described below.

Referring now to FIGS. 1 and 2, the transmission 16 can be any suitabletype of vehicle transmission such as a discrete-speed automatictransmission, a continuously variable automatic transmission, or anyother suitable transmission of any kind. The transmission 16 includes aninput shaft 24 and can include a coupling 26 to couple the input shaft24 to the output shaft 20 of the prime mover 14. The coupling 26 can beany suitable type of wet or dry coupling such as a torque converter, oran exemplary torsional-vibration damper as shown. For example, thecoupling 26 can be a dry damper and can include an input element 28connected to the prime mover output shaft 20 in any suitable manner suchas by bolts 30. The coupling 36 can also include an output element 32connected to the transmission input shaft 24 in any suitable manner,such as by a splined connection 34. The coupling 26 can further includedampening elements 36, such as springs, interposed between the inputelement 26 and output element 32 to provide a dampened connection.

The transmission 16 can also include a torque conversion portion 38 suchas motors, gearsets, pulleys and sheaves, or other speed reducers, orany combination thereof. The torque conversion portion 38 can providemechanical advantage by reducing speed and increasing torque between thetransmission input shaft 24 and an output shaft 40 of the transmission16.

The transmission 16 also includes an exemplary pump 42 to deliverpressurized hydraulic fluid to other portions of the transmission 16such as the torque conversion portion 38 for lubrication and/oractuation of transmission elements like clutches and pistons therein(not shown). The pump 42 can include a fixed element such as a stator 44and an input element such as a rotor 46 positioned within the stator 44.The pump 42 can be any suitable fluid pumping device such as a gerotorpump, vane pump, turbine pump, or any other pump of any kind.

The transmission 16 further includes a pump drive 48 to drive the pump42, whether the prime mover 14 is operating or not. The pump drive 48includes a transmission input torque member, such as the transmissioninput shaft 24, which carries prime mover torque. The transmission inputtorque member can be a solid shaft as shown or a hollow shaft or tube, ahub, or any other suitable torque carrying element. The pump drive 48also includes a source of pump input torque, such as a motor 50.

The motor 50 can be any suitable device to create torque, such as anelectric motor. For example, the electric motor 50 can include a stator52, windings 54, and a rotor 56 coupled to a torque transmitting member58 to apply torque directly to the transmission pump 42. The torquetransmitting member 58 can be any suitable component(s) to carry torquefrom the electric motor 50 to the pump 42. The torque transmittingmember 58 can include an outer ring 60 coupled to an inner hub or pumpinput torque member 62 by a spoke or web 64, which can be integrallyformed with the ring 60 and pump input torque member 62.

The pump input torque member 62 can be any suitable component forcarrying torque, such as the hollow shaft as shown in FIG. 2. The pumpinput torque member 62 is coaxial with and circumscribes thetransmission input shaft 24 and can be coaxially coupled to the innerpump element or rotor 46 in any suitable manner such as using a splinedconnection 66 as shown in FIG. 2. But the pump rotor 46 and pump inputtorque member 62 can instead be coupled in any other suitable fashionincluding being integrated together as a unitary component. Moreover,the motor rotor 56 and pump input torque member 62 can be similarlycoupled in any suitable fashion including being integrated together as aunitary component.

Referring to FIG. 2, the pump drive 48 can be housed within a pump drivehousing 68 to provide support for, and enclose, the pump drive 48. Thepump drive housing 68 can be carried by a transmission bell housing 68that is carried by a transmission case 70. The stator 52 can be carriedby the pump drive housing 68 in any suitable manner, such as using asnap ring 74 and/or a press fit or splined connection. The motor rotor56 is rotatable with respect to the stator 52 and is carried by thetorque transmitting member 58 in any suitable fashion, such as by a snapring 76 and/or a press fit or splined connection. Any suitable bearing78 can be interposed between the pump input torque member 62 and aportion of the housing 66 to provide support for the housing 66. Also,any suitable seal 80 can be interposed between the transmission inputshaft 24 and another portion of the housing 66, and another suitableseal 82 of any kind can be interposed between a flange of the pump drivehousing 68 and a portion of the bell housing 70 to provide a sealedenvironment for the pump drive 48. The seals 80, 82 enable the pumpdrive 48 to operate in a sealed environment and enables use of the drydamper 26 as opposed to a wet damper.

The pump drive 48 further includes an overrunning clutch 84 disposedbetween the pump input torque member 62 and the transmission input shaft24 to carry torque from the transmission input shaft 24 to the pumpinput torque member 62. The overrunning clutch 84 is also known as afreewheel or one-way clutch and, generally, is a machine element forconnection and disconnection of other elements in a transmission.Overrunning clutches are well known to those skilled in the art and anysuitable type of overrunning clutch can be used such as a sprag, spring,roller, ball, pawl-and-ratchet clutch, and/or the like. The overrunningclutch 84 can be carried by the pump input torque member 62 and/or theinput shaft 24 and can be axially trapped along the input shaft 24 by asnap ring 86 with a thrust washer 88 disposed therebetween.

As used with the pump drive 48, the overrunning clutch 84 enables theinput shaft 24 to be disengaged from the pump input torque member 62when the pump input torque member 62 rotates faster than the input shaft24, such as when the prime mover 14 is not rotating or is idlingrelatively slowly. In other words, the overrunning clutch 84 has twofunctions: 1) it engages to lock the transmission input shaft 24 and thepump input torque member 62 together when the prime mover 14 isoperating above a threshold speed to provide indirect driving to thepump 42; and 2) it releases to permit the pump input torque member 62 toprovide direct driving to the pump 42 by overrunning the transmissioninput shaft 24 when the prime mover 14 is not rotating or is rotatingbelow the threshold speed, i.e. more slowly than the threshold speed ofthe pump input torque member 62.

Accordingly, the pump 42 can be driven directly by the pump's electricmotor 50 through the pump input torque member 62, and/or indirectly bythe prime mover 14 through the overrunning clutch 84, depending on whichsource of torque is rotating faster at any given time. For example, atany prime mover speed that is less than sufficient to maintain thethreshold pump speed, the electric motor 50 can be activated to rotatethe pump 42 at the threshold speed or greater until the prime moverspeed increases to a level sufficient to maintain or exceed thethreshold speed again. At that point, the electric motor 50 can bedeactivated, such as to a standby mode, until the prime mover or pumpspeed again falls below the threshold speed, which can be any suitablevalue such as about 2,200 RPM. The motor 50 can be placed in standbymode to avoid conflicts wherein the motor 50 and prime mover 14simultaneously attempt to regulate the speed of the pump 42.

Referring now to FIG. 3, the electric motor 50 and its drive system 100are shown schematically. The electric motor 50 is a sensorless brushlessdirect current (SBLDC) motor that does not require position or speedsensors. Such sensors can be used but are not desired because the drivesystem 100 for the electric motor 50 can be used to sense motor terminalvoltages and determine the speed and position of the rotor 56 based onthe sensed motor back EMF voltages, even when the motor 50 is inactiveor in a standby mode. The motor 50 may be in standby mode at any time,such as when prime mover speed is above the threshold speed formaintaining suitable transmission pump output.

The motor 50 is shown with its stator 52, windings 54 including threephase windings 54 a, 54 b, 54 c wound on the stator 52, and rotor 56having magnetic poles N, S in rotational proximity to the windings 54.Each of the phase windings 54 a, 54 b, 54 c is connected to an exemplaryinverter circuit 102 that powers the motor 50. A filter capacitor C canbe placed in parallel with the inverter circuit 102, and electricity issupplied to the inverter circuit 102 from a DC voltage source V_(dc),such as one or more DC batteries, fuel cell(s), generator(s), powerconverter(s), and/or the like.

In the exemplary inverter circuit 102, there are two or more commutatingswitches corresponding to each phase winding 54 a, 54 b, 54 c forcommutating the phase windings 54 a, 54 b, 54 c of the motor 50. Eachset of switches is disposed in series across high and low sides of theinverter circuit 102. The first phase A and phase winding 54 a, areconnected between a first high side switch Q1 and a first low sideswitch Q4, the second phase B and phase winding 54 b are connectedbetween a second high side switch Q2 and a second low side switch Q5,and the third phase C and phase winding 54 c are connected between athird high side switch Q3 and a third low side switch Q6. The switchesQ1-Q6 can be any suitable switching devices, such as IGBTs, MOSFETs, orany other suitable semiconductor or transistor devices. Also in theinverter circuit 102, respective freewheeling diodes D1, D4, D2, D5, D3,D6 are connected in reverse parallel with the switches Q1, Q4, Q2, Q5,Q3, Q6. Those skilled in the art will recognize that the switches Q1-Q6can include integrated freewheeling diodes, instead of having thefreewheeling diodes D1-D6 provided separately.

In an inverter active mode, the inverter circuit 102 selectively appliesphase voltages V_(a), V_(b), V_(c) to one or more of the windings 54 a,54 b, 54 c, thereby causing phase currents I_(a), I_(b), I_(c) to flowthrough the windings 54 a, 54 b, 54 c, to energize the windings 54 a, 54b, 54 c. The windings 54 a, 54 b, 54 c include inductance componentsL_(a), L_(b), L_(c) and resistance components R_(a), R_(b), R_(c).

Even when the inverter circuit 102 is in an inverter inactive mode,rotation of the rotor 56 produces back electromagnetic force (EMF)voltages e_(a), e_(b), e_(c) in the phase windings 54 a, 54 b, 54 c. Tofacilitate sensing of the back EMF voltages e_(a), e_(b), e_(c) in thewindings 54 a, 54 b, 54 c during the inverter inactive mode, a bank ofresistors 104 is placed between the inverter circuit 102 and the motor50 between three phases A, B, C and ground. The bank of resistors 104includes at least one first resistor R_(x) connected to the first phase,at least one second resistor R_(y) connected to the second phase, and atleast one third resistor R_(z) connected to the third phase. The valuesof the resistors R_(x), R_(y), R_(z) can be the same, and can beselected to yield good signal-to-noise ratios and voltage matchingbetween measured circuits and control circuits. Those skilled in the artwill recognize that the resistor values can be chosen on a case-by-casebasis depending on the motor specifications and the like.

High voltage control circuitry is connected to the phases A, B, Cbetween the bank of resistors 104 and the inverter circuit 102. First,voltage scaling circuitry 105 can be placed in communication with thephases A, B, C just downstream of the inverter circuit 102. Second, abank of clamping circuits 106 can be placed between the phases A, B, Cand ground. Third, a selector 107 is placed downstream of the clampingcircuits 106 to select from among the three phases A, B, C depending onthe switching state of the inverter circuit 102. Fourth, any suitablesignal conditioning module 108 can be placed downstream of the selector107. Fifth, an analog-to-digital (A/D) converter 110 can be placeddownstream of the signal conditioning module 108 to convert analogvalues of phase voltages of selected phases into digital values.Finally, any suitable digital isolation 112, such as opto-couplers orthe like, can be placed downstream of the A/D converter 110 for suitablecoupling to a lower voltage controller 114.

The controller 114 can include commutating logic and/or circuits, whichproduce output signals for triggering the power electronics switchesQ1-Q6 depending on the determined instantaneous rotor position of themotor 50 to thereby commutate the phase windings 54 a, 54 b, 54 c of themotor 50. More specifically, the controller 114 can include any suitabledevice, circuits, software, and/or the like for receiving detected phasevoltages, determining change rate and commutation time of the phasevoltages, further processing such information, and outputting selectionsignals to the selector 107 and gate driver signals to a gate driver116. The gate driver 116 can be circuitry that receives output PulseWidth Modulation (PWM) signals from the controller 114 and controls theturn-on and turn-off of the power switches Q1-Q6 in the inverter circuit102 so as to commutate the motor 50.

The controller 114 can include any suitable processor(s) 118 configuredto execute control logic that provides at least some of thefunctionality for the phase switching. In this respect, the processor118 may encompass one or more processing units, microprocessors,micro-controllers, discrete logic circuit(s) having logic gates forimplementing logic functions upon data signals, application specificintegrated circuits (ASIC) with suitable logic gates, complexprogrammable logic devices (CPLD), programmable or field-programmablegate arrays (PGA/FPGA), any combinations of the aforementioned, and thelike. The processor(s) 118 may be interfaced with any suitable memory120, which can include any medium configured to provide at leasttemporary storage of data and/or software or instructions that provideat least some of the functionality of the switching and that may beexecuted by the processor 118. The controller 114 may also include anyother suitable devices or modules, such as ancillary devices likeclocks, power supplies, and the like.

Moreover, any other suitable devices can be placed in communication withthe controller 114, such as one or more sensor(s), other controllers, orthe like. In one example, the controller 114 can be coupled to anysuitable output coupling module 122 to suitably couple the lower voltageprocessor 118 to the higher voltage selector 107. The coupling module122 can include any suitable devices such as digital isolation,digital-to-analog converters, and/or the like. In another example, aninput device 124 such as a prime mover speed sensor or a transmissioninput shaft speed sensor can be used by the controller 114, such as todetermine when the rotational speed of the prime mover 14 and/or pump 42falls below or raises above the threshold speed. In another example, theinput device(s) 124 can include a prime mover controller, transmissioncontroller, or any other vehicle controller of any kind. In a furtherexample, the devices 124 can include transmission pressure sensors,throttle position sensors, and/or the like.

When the inverter 102 is active or in an inverter active mode, at anygiven moment two motor phases are conducting and a third phase is idle.In one example, when phase A and phase B are conducting, such as byturning on the power switches Q1 and Q5, phase C is the next phase to beenergized, such as by turning on power switch Q6. The time instant forturning on power switch Q6 is determined based on the back EMFzero-crossing point of phase C. The back EMF in phase C is readilyextracted using the voltage equations given in Eqs. 1 or 2 depending onthe instant when the terminal voltage is sampled.

Referring to the exemplary circuitry in FIG. 3, and neglecting phasewinding imbalance and the voltage drops across the power switches Q1 andQ5, the phase C terminal voltage is:

$\begin{matrix}{V_{c} = {{\frac{3}{2}e_{c}} + \frac{V_{dc}}{2}}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

-   -   when both Q1 and Q5 are “on”, and

$\begin{matrix}{V_{c} = {\frac{3}{2}e_{c}}} & {{Eq}.\mspace{14mu} 2}\end{matrix}$

-   -   when Q1 is “off” and Q5 is “on”, or D4 is freewheeling.        Hence, the phase C back EMF signal e_(c) can be extracted by        sensing phase C terminal voltages and/or V_(dc)/2, also known as        virtual neutral point voltage of a Y-connected electric motor,        depending on the time instant for terminal voltage sampling. The        phase terminal voltages are suitably scaled down and clamped for        processing in the signal electronics TTL level. For example, the        voltage scaling circuit 105 and clamping circuit(s) 106 may be        used.

A suitable phase terminal voltage is selected, such as by the selector107, and communicated to the controller 114 for back EMF zero-crossingdecoding, which can be carried out by any suitable zero-cross decodinglogic. Zero-cross decoding logic is generally known to those of skill inthe art to determine which phase terminal voltage is to be monitoredbased on which PWM duty cycle commands are being sent to the gate driver116 by the processor 118. For instance, when phase A and phase B areconducting at a given time, phase C terminal voltage is selected to bemonitored.

Suitable signal conditioning is performed by the signal conditioningcircuit 108 for filtering out electrical noise in the suitably selectedphase terminal voltage signal. The A/D converter 110 converts theselected phase terminal voltage signal from analog form to digital formto the digital isolation 112 which in turn isolates the motor terminalvoltage signal referenced to the high voltage ground to low voltageground.

The controller 114 receives the selected phase terminal voltage signaland determines the time instant for back EMF zero crossing event. Thecontroller 114 further uses the detected back EMF zero crossing event toestimate the operating position and/or speed of the motor 50 anddetermine when to turn on the corresponding phase in the form of PWMduty cycles, such that the energizing of motor phases are synchronizedwith the magnetic field created by the magnets on the rotating rotor foruseful electromagnetic torque production. The electromagnetic torquerequired is determined by any suitable speed regulator in controller 114in order to achieve a commanded speed setpoint that motor 50 has tooperate at. Speed regulators are known to those skilled in the art andcan include circuitry, software modules, and/or the like.

The controller 114 sends the PWM duty cycle commands to the gate driver116 on the high voltage side via voltage isolation 126. The gate driver116 amplifies the received PWM duty cycle commands and sends them to theappropriate gate pins of the corresponding power switches in theinverter 102 to energize the corresponding motor phases.

Back EMF zero crossings can also be detected when the inverter isinactive, preferably using the bank of resistors 104 for referencing thephase terminal voltages to ground, and any suitable motor phase terminalvoltage sensing and conditioning circuitry. For example, any suitablevoltage scaling, clamping, and signal conditioning circuitry and/ordevices may be used, such as that shown in FIG. 3. In other words, thecontroller 114 can determine motor rotor position and/or speed usingzero-crossings of the back EMF voltages e_(a), e_(b), e_(c) even whenthe inverter circuit 102 is inactive, such as when the motor 50 is in astandby mode but the rotor 56 is still rotating. For example, becausethe rotor 56 is coupled to the rotating pump input torque member 62, therotor 56 rotates and back EMF signals are thus produced. The bank ofresistors 104 suitably grounds the phases A, B, C when the invertercircuit 102 is inactive such that useful back EMF signals and/or phaseterminal voltage signals with proper reference to high voltage groundfrom the phases can be sensed. Accordingly, useful back EMFzero-crossings can be determined in similar fashion as described aboveand, thus, motor positions and speeds can be determined even when theinverter is inactive.

The controller 114 determines when to operate the motor 50 so as tooperate the pump 42 in an electric motor active mode. For example, thecontroller 114 can activate the motor 50 when the prime mover is notoperating or is not rotating fast enough to properly power the pump 42.Also, the controller 114 can activate the motor 50 when transmissiontorque demand is below a certain threshold, and transmission clutchpressure and transmission cooling demand are below respectivethresholds. Otherwise, when prime mover speed is sufficient to suitablyoperate the pump 42 at or above the pump threshold speed, then thecontroller 114 can place the motor 50 in its standby mode to allow theprime mover 14 alone to drive the pump 42, such as by deactivating theinverter 102 for example by opening all power switches Q1-Q6. Thecontroller 114 can determine pump speed as a function of time and itsdetermination of its rotor position by way of the back EMF signals.Also, the controller can determine pump speed as a function of primemover speed signals received a prime mover speed sensor such as theinput device 124.

It is desirable to ensure a smooth transition between driving the pumpby the prime mover 14 and by the electric motor 50. Accordingly, thedrive system controller 114 needs to know the rotational speed andposition of the rotor of the electric motor 50 even when the inverter102 is inactive or in standby mode. When the drive system controller 114detects that the pump and/or motor speed has dropped below a pre-definedthreshold, the controller 114 immediately exits standby mode andprovides power to the motor 50 to drive the pump 42 at or above thethreshold speed. Otherwise, the transmission may lose fluid pressure andtransmission gear engagement might be lost. Because the controller 114knows the position of the motor rotor 56 at any given time via the backEMF signals, the inverter 102 and motor 50 can be instantly activated sothat pump speed does not drop below the threshold speed.

Operation of the electric motor 50 from standby mode is different frominitial start-up of the electric motor 50 from standstill. When theelectric motor 50 is started from standstill, the drive systemcontroller 114 does not initially know the rotor position and, thus,suitable open loop ramp up control is used to rotate the motor rotorbeyond a certain minimum speed above which the drive system controller114 can begin to reliably detect back EMF zero crossings. This start-upprocess typically takes several hundred milliseconds.

While certain preferred embodiments have been shown and described,persons of ordinary skill in this art will readily recognize that thepreceding description has been set forth in terms of description ratherthan limitation, and that various modifications and substitutions can bemade without departing from the spirit and scope of the invention. Byway of example without limitation, while the electric motor has beenshown as being adapted for a transmission pump, it could be adapted forany other suitable device(s) of any kind. The invention is defined bythe following claims.

1. A pump drive for a vehicle transmission pump, comprising: atransmission input torque member operable to carry prime mover torque; asource of pump torque including a pump input torque membercircumscribing the transmission input torque member to apply torque tothe transmission pump, wherein the source of pump torque includes anelectric motor and an inverter circuit coupled to the electric motor anda controller in communication with the electric motor, and wherein thecontroller is configured to activate the inverter circuit and electricmotor to drive the pump when the pump speed is less than a thresholdspeed, and is configured to deactivate the inverter circuit and electricmotor to allow the prime mover torque to drive the pump when the pumpspeed is greater than the threshold speed; and an overrunning clutchinterposed between the pump input torque member and the transmissioninput torque member to carry the prime mover torque from thetransmission input torque member to the pump input torque member.
 2. Thepump drive of claim 1, wherein the transmission input torque member is atransmission input shaft.
 3. The pump drive of claim 1, wherein theelectric motor is a sensorless brushless direct current electric motor.4. The pump drive of claim 3, wherein the controller determines positionand speed of the electric motor using back EMF voltages from theelectric motor.
 5. The pump drive of claim 3, wherein the electric motorincludes a rotor, and the source of pump torque further includes atorque transmitting member that is coupled to the rotor and includes thepump input torque member.
 6. The pump drive of claim 1, further whereinthe pump input torque member is coupled to a rotor of the transmissionpump by a splined connection.
 7. The pump drive of claim 1, furthercomprising: a pump drive housing; a bearing interposed between the pumpdrive housing and a portion of the pump input torque member to supportthe pump drive housing; and a seal disposed between the pump drivehousing and the transmission input torque member.
 8. A vehicletransmission, comprising: a transmission pump having an input element; apump drive including an electric motor coupled to a pump input torquemember and being operable to apply torque directly to the input elementof the transmission pump, wherein the pump drive further includes aninverter circuit coupled to the electric motor and a controller incommunication with the electric motor and adapted to activate theinverter circuit and electric motor to drive the pump when the pumpspeed is less than a threshold speed, and deactivate the invertercircuit and electric motor to allow a prime mover torque to drive thepump when the pump speed is greater than the threshold speed; atransmission input shaft operable to receive prime mover torque; and anoverrunning clutch disposed between the transmission input shaft and thepump input torque member of the pump drive and operable to carry theprime mover torque to the pump input torque member.
 9. The vehicletransmission of claim 8, further comprising: a transmission bellhousing; a pump drive housing carried by the bell housing; a bearinginterposed between the pump drive housing and a portion of the pumpinput torque member to support the pump drive housing; a first sealdisposed between the pump drive housing and the transmission inputshaft; and a second seal disposed between pump driving housing and thetransmission bell housing.
 10. The vehicle transmission of claim 9,further comprising a torsional-vibration damper coupled to thetransmission input shaft and to an output shaft of a transmission primemover.
 11. The vehicle transmission of claim 10, wherein the damper is adry damper.
 12. The vehicle transmission of claim 8, wherein theelectric motor comprises a sensorless brushless direct current electricmotor.
 13. The vehicle transmission of claim 12, wherein the controllerdetermines position and speed of the electric motor using back EMFvoltages from the electric motor.
 14. A vehicle powertrain, comprising:(a) an internal combustion engine including an engine output shaft; and(b) a transmission coupled to the engine and comprising: (1) atransmission input shaft operable to receive engine torque from theermine output shaft; and (2) a vibration damper coupled between thetransmission input shaft and the engine output shaft; (3) a transmissionpump having an input element; (4) a puma drive operable to apply torqueto the input element of the transmission pump, the pump drive comprisinga sensorless brushless direct current electric motor having a stator,windings, and a rotor, a pump input torque member coupled (i) to therotor of the electric motor and (ii) to the input element of thetransmission pump, and an overrunning clutch disposed between thetransmission input shaft and the pump input torque member that isoperable to carry the engine torque to the pump input torque member; andwherein the pump drive further includes an inverter circuit coupled tothe electric motor and a controller in communication with the electricmotor, wherein the controller determines position and speed of theelectric motor using back EMF voltages from the electric motor,activates the inverter circuit and electric motor to drive the pump whenthe pump speed is less than a threshold speed, and deactivates theinverter circuit and electric motor to allow the engine torque to drivethe pump when the pump speed is greater than the threshold speed. 15.The pump drive of claim 1, wherein the electric motor comprises asensorless brushless direct current electric motor and the controllerdetermines pump speed using back EMF of the electric motor indetermining when to activate and deactivate the electric motor.
 16. Thevehicle transmission of claim 8, wherein the electric motor comprises asensorless brushless direct current electric motor and the controllerdetermines pump speed using back EMF of the electric motor indetermining when to activate and deactivate the electric motor.
 17. Thepump drive of claim 1, wherein the electric motor comprises a threephase electric motor and further comprising a bank of resistors betweenthe inverter circuit and the electric motor including at least oneresistor connected to each one of the phases of the electric motorfacilitating sensing of back EMF voltages when the inverter circuit isdeactivated.
 18. The vehicle transmission of claim 8, wherein theelectric motor comprises a three phase electric motor and furthercomprising a bank of resistors between the inverter circuit and theelectric motor including at least one resistor connected to each one ofthe phases of the electric motor facilitating sensing of back EMFvoltages when the inverter circuit is deactivated.
 19. The powertrain ofclaim 14, further comprising a bank of resistors between the invertercircuit and the electric motor including at least one resistor connectedto each phase of the electric motor.